This invention relates generally to x-ray diagnostic medical imaging and, more particularly, to methods and apparatus for x-ray images.
In many x-ray imaging system configurations, an x-ray source projects an area beam which is collimated to pass through a region of interest of the object being imaged, such as a patient. The beam, after being attenuated by the object, impinges upon an array of radiation detectors. The intensity of the radiation beam received at the detector array is dependent upon the attenuation of the x-ray beam by the object. In a digital detector, each detector element, or pixel, of the array produces a separate electrical signal that is a measurement of the beam attenuation at that location of the detector. The attenuation measurements from all the detector pixels are acquired separately to produce a transmission profile.
In a typical x-ray imaging system, a patient is positioned between an x-ray tube and an image receptor having a planar imaging surface, such as an x-ray film or a digital solid state detector. The tube projects a beam of x-radiation toward the detector surface and through the body structure of the patient to be imaged. The area of projected radiation, which is incident on the detector, defines the active imaging area (AIA). Generally, the x-ray beam field, or field of view (FOV), which is defined herein to be the intersection of the projected beam and the detector plane, must be coincident with, or lie within, the boundaries of the detector surface in order to avoid loss of image data. The FOV may be adjusted by rotating or tilting the tube to vary the direction of the projected x-ray beam, and also by operating a collimator to vary the width and length dimensions of the x-ray beam. Further adjustments may be made by linear translation of the tube and/or the detector Combining adjacent images to achieve an image longer than the length of the detector requires some movement on the part of the x-ray source between exposures. Due to the length of an exposure, the images are subject to distortion or blurring from motion of the source during exposure as well as vibrations of the source if the unit is stopped, both resulting in lower image quality. In addition, pasting adjacent images typically requires some overlap, which results in extra dose to the patient at some positions. Also, because of overlap at this region, there is a different signal to noise ratio in this region than in the rest of the image which can be seen as bands of high resolution on the final image.